Solve the great soluble phosphorus mystery

As early as 2008, Joe Nester knew something wasn’t adding up correctly when it came to phosphorus levels in lakes and streams, and the number and intensity of algal blooms that were occurring in his area. Nester, with nearly four decades of experience as an agronomist, operates Nester Ag LLC near Bryan, Ohio. He works with farmers in Ohio and Indiana.

Phosphorus is supposed to stay put and move very little after application. It’s nitrogen that moves. Nester began to wonder if that relationship is still true today.

“Less fertilizer was applied over a 10- year period in the Lake Erie Basin than before, yet we still wound up with a serious algal bloom in August of 2014,” he notes. “Our problem really isn’t with algae. It’s with the toxins that these blooms produce,” Nester says. “When officials shut off the water supply for the city of Toledo [Ohio] for an entire weekend in 2014, it got everyone’s attention.”

Farming and commercial fertilizer aren’t the only potential source of phosphorus that could wind up in Lake Erie. There is a whole list of possible sources, but agriculture is definitely on the list.

Identify source of changeNester knew that what was happening didn’t make sense using traditional thinking. What had changed in the past 10 to 20 years that could explain what he saw?

Then he ran across information about how rain was no longer as acidic as it once was. The typical acidity of rain today, at least in his area, has a pH of about 6.2 to 6.3. It was once considerably lower.

The primary source of acid rain is the deposition of sulfur dioxide and nitrogen dioxide in the atmosphere, Nester observes. The lightbulb went on!

“The Clean Air Act passed by Congress more than two decades ago was working,” Nester realized. Sulfur emissions were way down. There was less nitrogen dioxide released into the air as well.

“The increase of pH in rainwater means it’s not as acidic now,” Nester notes. “The thing about pH is that a relatively small change in the number on the pH scale has a big impact on how much acidic material goes into the environment.” For example, a pH of 4.3, which is where acid rain was before the Clean Air Act began, is many times more acidic than a pH of 6.3, he says.

Phosphorus is more soluble in water as pH increases. According to the Purdue University Corn & Soybean Field Guide, once soil pH nears 6.0 or higher, phosphorus is much more available.

“What’s changed is the pH of rain,” Nester explains. ‘”That means phosphorus is likely to be more soluble than it once was. If it’s more soluble, it can move more than we once thought possible.”

That’s why when agronomists began trying to explain what happened after the Toledo algal bloom, the term “dissolvable phosphorus” appeared. Even if less phosphorus was applied, more of it could go into a solution than before.

Change managementIdentifying that the environment has changed was the first step. The next step for Nester is helping farmers learn how to manage in a new environment.

“We’re very big on promoting the 4R concept,” he says.

The 4R concept boils down to applying the right form of fertilizer at the right rate at the right time in the right place. “It’s caused us to rethink how we do things,” Nester says. “We now must manage phosphorus knowing that at least a portion of it can dissolve, and be more subject to movement than we once thought.”

NO LONGER FREE: Mike Starkey’s dad didn’t worry about sulfur for corn. It was in the air for the taking. Since that’s no longer true, Starkey (standing) tells his Chinese guests that he pays attention to S levels.

Sulfur is no longer freeMike Starkey, Brownsburg, Ind., recently hosted a group of young scientists from China in the toolshed on his farm. Most of these visitors work in some facet of environmental science in China. Their ears perked up when the no-till, cover crop enthusiast talked about the environment in his area.

“Our Congress passed the Clean Air Act many years ago, and manufacturers, primarily power-producing plants, were required to take many measures to reduce emissions,” he explained. One element that they were required to remove was sulfur.

“I want clean air as much as anyone else. What the legislation did worked — it cleaned up the air. But that has also affected how I farm.”

Huh? Yes, actions have consequences. He soon explained that his dad and granddad never worried about sulfur, a secondary but important nutrient, for corn. There was enough sulfur in the air from these emissions to satisfy the plant’s needs for sulfur. You didn’t read articles about S back then, and no one talked much about it because corn didn’t respond to adding sulfur, Starkey explained.

That’s no longer the case. “We occasionally see sulfur deficiencies now,” says Joe Nester, a crops consultant with Nester Ag LLC in Bryan, Ohio. He has also visited Starkey’s toolshed and talked to farmers. Starkey typically follows Nester’s advice. One of the ways Starkey applies nutrients like sulfur is through foliar application. He uses Y-Drops on his high-clearance sprayer, equipped with undercover devices to spray above the ground when corn is in the V12 to V14 stage.

Nester notes that if you look at maps showing sulfur deposition from atmospheric sulfur in the Midwest from different periods of time, there is a marked change. “There was still considerably more sulfur emissions in 2005 than there is today,” he notes. “The maps for sulfur deposition today show far less sulfur being emitted into the atmosphere. As a result, it’s another nutrient we need to consider when putting together soil fertility plans for corn.”